<!DOCTYPE html>
<html lang="zh">
<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="ie=edge">
	<title></title>
</head>
<body>
	<script>
		var a=prompt('请输入运算法则')
		var res=(eval(a))
		alert(res)
	</script>
</body>
</html>